Organic Light Emitting Diode (OLED) has become a popular field in the flat panel display researching. As a current-controlled light-emitting device. OLED has being increasingly applied in the field of high-performance display, due to the characteristics such as self-emission, fast response, wide viewing angle and capable of being fabricated on flexible substrate. Currently, in the display field of phone, PDA, digital cameras and the like, OLED has begun to replace the traditional LCD (Liquid Crystal Display) display. Pixel driving circuit design is a key technical content of OLED display, which has important significance of research. Different from TFT (Thin Film Transistor)-LCD which controls brightness by using stable voltage, OLED is of a current driving type which requires stable current to control light emitting. Due to process technology, device aging and other reasons, in an original 2T1C driving circuit (including two thin-film transistors and a capacitor), the threshold voltage on the driving TFTs of the respective pixels is uneven, thereby the current flowing through the OLED in each pixel is varied, the display brightness is uneven, thus affecting the display performance of the entire image.